Why Detroit air meets ozone standard but West Michigan does not

The DTE Monroe coal-fired power plant stacks backdrop the campground at William C. Sterling State Park on Lake Erie in Frenchtown Township, Mich., May 20, 2023. (Garret Ellison | MLive)

The air over Muskegon this week is unhealthy enough for certain people, such as those with a respiratory disease like asthma, that forecasters issued an alert.

The problem is ozone, a naturally occurring gas that protects the Earth from ultraviolet radiation in the upper atmosphere but which can trigger chest pain, coughing, throat irritation and inflame respiratory problems when it forms low enough where people can breathe it.

Ozone levels in parts of West Michigan are helping keep the area out of "attainment" with federal air quality standards; a frustrating status for the region's business community because the designation may translate to tighter restrictions on emitting air pollutants such as nitrogen oxide (NOx), a precursor chemical that helps create ground level ozone.

Meanwhile, the U.S. Environmental Protection Agency (EPA) this year lifted a non-attainment designation for seven metro Detroit counties at the request of state regulators, who say ozone levels in southeast Michigan have improved enough over the past two decades to now meet federal standards.

That means air over an industrialized region with a major transportation corridors and a large population meets federal standards while air over parts of the Lake Michigan coast with fewer people, automobiles and industry does not.

It's an incongruity and the reason for it is Chicago.

"I think it's well accepted that the cause of those emissions are coming, for the most part, from across the lake," said Tom Shanley, an air quality evaluation manager at the Michigan Department of Environment, Great Lakes and Energy (EGLE).

The lakeshore has struggled to meet federal air quality standards for several years due to emissions from across Lake Michigan which are blown east by prevailing wind patterns. In November, Berrien County and the western half of Muskegon and Allegan counties were downgraded from marginal to moderate "non-attainment" for ground level ozone.

Ozone, which helps form smog, develops on hot, stagnant days when NOx and other air pollutants such as volatile organic compounds (VOCs) bake together while blowing over the lake from Chicagoland and parts of Indiana.

Such conditions resulted in an Air Quality Action Day alert for Tuesday, May 30 and Wednesday, May 31 across much of southwest, west and northwest lower Michigan.

On such days, certain people are encouraged to limit prolonged exertion outdoors and asked to reduce activities which can help create ozone, such as driving and burning fossil fuels.

Air Quality alert days are among a series of measures the state expects to include in a plan to regain ozone attainment in West Michigan that must be submitted to EPA this year.

That plan is expected to require use of reasonably available control technology (RACT) at industrial sources of ozone-forming emissions, such as factories and power plants. Additional regulatory steps may include ozone source reviews and limits on use of certain solvents, coatings and adhesives that release NOx and VOCs.

Regional businesses aren't happy about that.

"Restrictions imposed on West Michigan due to the nonattainment designation will have little to no impact on the quality of our air in this region, while having a negative impact on growth and employers," said Rick Baker, president of the Grand Rapids Chamber of Commerce, this month. "We look forward to working with our federal partners to correct this."

Shanley said most ozone in West Michigan is caused by emissions "transport" from over the lake, but the area does have its own sources and a localized air circulation in the form of lake breezes which is "often the cause of some of our elevated values along the lakeshore."

Detroit finally ‘attains’ ozone compliance

West Michigan isn't the only part of the state under an ozone alert this week. Air quality is also poor over southeast Michigan, including metro Detroit, Flint and Ann Arbor.

Unlike the lakeshore, ozone is no surprise in the Detroit area. Michigan's most populous and heavily industrialized region has plenty of air pollution sources.

But regulators say ozone in metro Detroit has been declining since the 1990s and the region now meets the EPA threshold for "attainment" under federal air quality standards developed in 2015, which EGLE considers a major achievement.

Shanley attributed the reductions to a market trend toward cleaner vehicles, phase-out of coal power plants and better emissions control technologies at industrial facilities.

"From my perspective, it's the mobile sector and it's the large coal burning sources," that contributed the most to the reduction, Shanley said.

This month, the EPA redesignated the seven county area encompassing Livingston, Macomb, Monroe, Oakland, St. Clair, Washtenaw and Wayne counties as in attainment based on air monitoring data collected by EGLE between 2019 and 2022.

Environmental groups don't agree with the conclusion.

In requesting the redesignation, EGLE asked EPA to exclude data collected last June 24 and 25 under an exemption for "exceptional events." Although one air monitor detected ozone over the threshold standard of 70-parts-per-billion, the state calculated it was due to wildfire smoke from Canada which had drifted over Michigan during an inopportune moment.

"We don't think EGLE should be in the business of avoiding protecting Detroit residents," said Nick Leonard, director of the Great Lakes Environmental Law Center.

The group disputes EGLE's conclusion that wildfire smoke skewed the reading and is considering a challenge to the redesignation. In a letter to EPA in April, the law center and 20 other Michigan environmental groups argued that the reductions in ozone were a "temporary downward blip due to cooler temperatures and higher humidity."

Moving the Detroit region back into ozone attainment means EGLE can avoid enacting stricter regulations on local industrial sources and vehicle emissions, Leonard said.

"I think it's clear they didn't want to take the additional regulatory steps they would be required to," he said.

The groups think that's a missed opportunity to ease the respiratory burden in Detroit, where asthma rates are disproportionally higher than elsewhere in Michigan. In 2022, Detroit was ranked No. 1 among U.S. cities with the highest prevalence of asthma and asthma-related emergency room visits and deaths by the Asthma and Allergy Foundation of America (AAFA).

The redesignation requires EGLE to ensure ozone levels stay within attainment, which the state plans to do through monitoring and existing regulation, according to its maintenance plan. The environmental groups think it's likely ozone levels will rise again, but EGLE does not.

"We fully expect that in southeast Michigan we’ll continue to see reductions both in emission and ozone concentrations," Shanley said.

In West Michigan, EGLE hopes a federal crackdown on emissions which cross state lines will reduce ozone concentrations along the lakeshore. A new EPA "good neighbor rule" is ratcheting down allowable NOx emissions from factories and power plants over the next six years.

"With some of the national efforts and efforts from our neighboring states, we do hope in the near future we’ll start to see reductions on the west side as well," Shanley said.

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Why Detroit air meets ozone standard but West Michigan does not